Rare earth fluoroaliphatic sulfonates

ABSTRACT

A METHOD IS DISCLOSED FOR THE PREPARATION OF ANHYDROUS FLUORIDES OF HIGH PURITY SUBSTANTIALLY FREE FROM OXYFLUORIDES OF TRIVALENT METALS OF GROUP IIIB OF THE PERIODIC SYSTEM PARTICULARLY OF SCANDIUM, YTTRIUM AND THE LANTHANIDE RARE EARTH METALS BY PYROLYSIS OF FLUOROALIPHATIC-SULFONATES OF THESE METALS. A PROCESS FOR PRODUCING THE LATTER SALTS WHICH ARE ISOLATED AS COMPLEXES WITH WATER OR ORGANIC MOLECULES IS ALSO DISCLOSED. THESE SALTS HAVE UNUSUAL SOLUBILITY PROPERTIES.

United States Patent O RARE EARTH FLUOROALIPHATIC SULFONATES Karl F.Thom, St. Paul,.Minn., assignor to Minnesota Mining and ManufacturingCompany, St. Paul, Minn. No Drawing. Original application Oct. 30, 1969,Ser. No.

872,726, now Patent No. 3,615,169. Divided and this application Jan. 25,1971, Ser. No. 109,579

Int. Cl. C07f /00 US. Cl. 260-429 R 2 Claims ABSTRACT OF THE DISCLOSUREA method is disclosed for the preparation of anhydrous fluorides of highpurity substantially free from oxyfluorides of trivalent metals of Group11111 of the periodic system particularly of scandium, yttrium and thelanthanide rare earth metals by pyrolysis of fluoroaliphatic-sulfonatesof these metals. A process for producing the latter salts which areisolated as complexes with water or organic molecules is also disclosed.These salts have unusual solubility properties.

This is a division of application Ser. No. 872,726 filed Oct. 30, 1969,now US. Pat. 3,615,169.

This invention relates to a method for forming fluorides of metals ofGroup IIIb of the periodic system in the di or trivalent condition andparticularly to a pyrolytic process for pyrolytically decomposingmetalic tris(fluoroaliph-aticsulfonates) to give metalic fluoridestogether with gaseous by-products which are swept away in an inert gassuch as N Ar or the like. This invention is also concerned withproduction of fluoroaliphatic-sulfonate salts and complexes thereof withwater and/or organic hetero-atom oxide ligands.

Four commercial processes have been disclosed and are described by J. H.Moriarty, Jr., J. of Metals, vol. 68, November 1968, pages 41-45. Theseprocesses react the desired oxide with HF or ammonium fluoride, or reactthe chloride with HF followed by dehydration of the hydrate of thefluoride.

Moriarty points out that the rare earth fluorides obtained cannot bedehydrated satisfactorily on an industrial scale. This conclusion issubstantiated by Wendlandt and Love, in Science 129, 342 (1959), inthermal gravimetric analysis studies of rare earth compounds. In thislatter case there is a continual decrease in weight rather than a breakin the decomposition curve corresponding to the loss of a definitenumber of moles of water. The formation of an oxyfluoride is observedbetween 600-690 C. The process does not result in a pure fluoride evenat temperatures of 900 C. Hence no previous process permits theformation of anhydrous fluoride. The presence of water in all previousinstances fosters the formation of oxyfluorides which contaminate therare earth fluoride.

In the present specification and claims the term rareearth includes thelanthanide rare-earths, yttrium and scandium. The preparation of purerare earth fluorides is important because they are used in electronicapplications, as catalysts, and as starting material for the preparationof rare earth metals. The use of lanthanum fluoride in infra-red opticsis described in US. Pat. 3,437,724. During metal preparation from thetrifluoride, any oxyfluoride which remains dispersed throughout themetal as a nonmetallic inclusion makes fabrication of the metalextremely difficult.

It is an object of this invention to produce fluorides of Group III!)trivalent metals in particular of scandium,

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yttrium and the lanthanides. A further object is to produce suchfluorides in essentially pure tri-fluoride form substantially free fromoxyfiuorides or hydrolysis products. Another object of the invention isto provide novel fluoroaliphatic sulfonate salts of III!) metals. Otherobjects will become apparent hereinafter.

It has been found that the thermal decomposition of rare earth metalsalts of fluoroaliphatic sulfonic acids, such as perfluoroalkane,perfluorocycloalkane and substantially fluorinated alkane andcycloalkane sulfonic acids, provides pure rare earth metal fluorides.Hetero atoms of O or N may occur in these sulfonic acids.

The salts of the rare earth metals are prepared by reacting the rareearth oxides which may be present only in the ore or as a crudeconcentrate with the required fluoroaliphatic sulfonic acids (described,for example, in US. 2,732,398). The salts are obtained as nonahydratesor complexes with organic hetero-atom oxide ligands of differentstructures. The complex salts are thermally decomposed between about 500and 1000" C. in an inert (argon or nitrogen) or reducing (hydrogen)atmosphere. The complexes with organic ligands appear to decompose atsomewhat lower temperatures.

In addition it is found that the decomposition of fluoroaliphaticsulfonic acids results in degradation with loss of the sulfonic groupand formation of the corresponding fluoroalkanoic acid fluoride:

argon M(0 so orzcrzomorntxmo h t MFs 502 XHzO CFQCFZCFZCOF whichhydrolyzes in the presence of more water:

The procedure of the invention yields a pure rare earth fluoride by thefollowing illustrative reaction in which M is a metal of the group ofscandium, yttrium and the lanthanides.

The reaction is often effected using the hydrated salt which seems notto interfere with forming an anhydrous metallic fluoride. The liberatedwater appears to be carried away in outgases before there is anyreaction with the metallic fluoride.

The hydrated rare earth metal perfluoroalkane sulfonate salts aresoluble in acetonitrile, water and certain oxygenated organic solventssuch as tetrahydrofuran, methanol, ethanol, isopropanol, acetone,methylethylketone and ethylacetate. The outstanding solubility of thehydrated rare earth trifluoromethane sulfonates makes them valuablehomogeneous catalysts and may aid in separation problems. They formnonahydrates and lose water under various methods of drying. Thus theneodymium trisperfluoromethane sulfonate nonahydrate yields theoctahydrate when dried over concentrated sulfuric acid and is furtheraltered to a dior trihydrate by drying under vacuum.

The hydrated salts are readily crystallized from solution and are thenobtained in a very pure form. The hydrated salts in alcoholic solutionreact with liquids such as four moles of hexamethyltriamine phosphineoxide, e.g.,

or five moles of N-methyl morpholine oxide to give precipitates ofcomplexes which are significantly soluble in such halogenated solventsas chloroform. The rare earth perfluoroalkane sulfonate salts containingwater or organic liquids are remarkable in their decomposition to givefluorides by breakdown of fluoroaliphatic sulfonic acids.

The crystal structures of the nonahydrated salts obtained 4 EXAMPLE 1Neodymium oxide (Nd O available from Molybdenum Corporation of America;99.9% pure) 10.0 gm. (29.7 mM.) is treated with 25 ml. H O in a Petridish. Freshly p the.reaction of mfodynilium oxide (Ndzoa) i 5 distilledtrifluoromethane sulfonic acid (CF SO' H-anhytrium oxide (Y O withtrifiuoromethane sulfonic acid drous) (27.0 mM.) is added drohwise tothe (CF3SO3H) were (leternlmedpy X'ray dlfiractlon. The stirred slurryand the oxide dissolves completely with compounds crystalhze wlth P P 9water m the evolution of heat. Additional water may be added ifdehexagonal System- The chemlcal Q of rare sired to moderate theexothermic reaction. The solution earth elements assures that all thetris salts of trifluoro- 10 is heated gently on a hot Plate to evaporatewater and the methane Su1fn 1c q shoulqhavq Smaller structures' pinksalt crystallizes. The resulting salt weighs 53.9 grn. The flu?rahPh?t1csulfomc aclds owhlch a used which indicates a slight excess of waterover the formula dude stralght and bfanciled 1 and 3 Nd(OSO CP] .9H O.The salt is dried in an oven at 130 alkane, cycloalkane SlllfOIllC acidsand also similar acids 0 for 48 hours The resulting product contains 478% 9I1ta1mng hydrogen atoms not On the clrbon H O 4.s2%-4.73% by KarlFisher Titration). This coracent to the sulfonic group, Many such acidsare available responds to Nd(OSO2CF3)3 1 65H2O from the literatureincluding those in which hetero atoms, A portion of this Salt (03541gm.) is heated to 6 C. e.g., oxygen and nitrogen, are included 1n thechains. Such in an alumina boat in a rapid stream of argon The decormhetero atoms generally exert very little influence on the ositioncontinues over a 4 hour period. The weight loss reactlons of the is67.68%. For the reaction:

Thermal decomposition of these hydrated salts or those complexed withoxygen containing organic ligands yields Nd(OSO CF .l.65H O NdF purerare earth fluorides. The purity of these salts is established byanalysis of the original rare earth perfiuorothe theoretical loss is67.70%. X-ray analysis shows that alkane sulfonate and by following theweight loss of these the residual product is pure NdF salts. The productis also corroborated by X-ray analysis. Other preparations (Examples2-7) are carried out in The by-product gases, COF and S0 are detected bythe same manner as Example 1 using 10.0 gm. of trivalent infraredanalyses. Flurodies prepared from organo-comrare earth oxide in eachcase and decomposing at 800 C. plexed salts may show slightdiscoloration which i bein argon atmosphere. The data obtained aretabulated believed to be due to traces of impurities carried by the low.Similar results are obtained using other inert gases, ligands. e.g., NExample 8 is carried out similarly using an at- The Group III!) metalsemployed as their fiuoroaliphatic mosphere of hydrogen at 1000 C. Theproduct is EuF Percent Pyrolysis weight E lgO loss forMFs, percent 8 erExample Salt Color drying Found Cale. X-ray 2 LQ(OSOIOFJ)3'XH2O 69.0468.71 LaF; 3 Pl'(OSO2CF3)3- H2O 69.12 68.93 PrF; 4-... sm(oSO1CF3)a'XH2O66.9 67.16 SmF; 5. Gd(OS0l F3)3'XH2O 68.4 66.8 GdF, 6. Y(OSO2CF3)3'XH2O77.3 75.7 Yr. 7 Eu(0s0iCF3)3-XHi0 70.1 68.3 Eur, E11(OS02CF3)I'XH1O 72.771.1 Eur,

)r perfluoroalkane sulfonates have atomic numbers from EXAMPLE 9 .1through 71.

For comparison the rare earth metal fiuorosulfonates indtrifluoroacetates are prepared by reaction of the same xide withfiuorosulfonic and trifiuoroacetic acids repectively. The lanthanum landneodymium fluorosulfoiates, La(SO F)( and Nd(SO F) are insoluble inorganic olvents and sparingly soluble in water. Pyrolysis of these altsin argon does not yield the fluoride, but instead gives xysulfates (La OSO and Nd O SO The salts of triluoroacetic acid are soluble in organicsolvents and water, ut during pyrolysis extensive foaming (COliberation) is ncountered. The resulting product is gray to black inolor and probably contains some oxide or carbon or a arbon compound.

The perfluoroalkane sulfonates employed in this inven- Ion are formed byreacting the oxide with fluoroaliphatic ulfonic acid according to thereaction.

VI) M O -l- 6HOSO R 2M (OSO RQ 3 +3H O here R, may be straight chain orbranched and is a fluosaliphatic radical of 1 to 18 carbon atoms whichmay Jntain catenary ether oxygen or tertiary amine nitrogen toms. Apreferred salt is M( OSO CF N -methylmorph0llne oxidehexamethylphosphoramide These are represented in formulae byabbreviations NMMO and HMPA respectively. The compositions, colors,decomposition points and analyses for C, H and O are tabulated below.Each decomposes to the pure fluoride. Naturally pyrolysis is more rapidat higher temperatures,

L M(OSO:CF:):

Analysis Calculated Found M.P.

Compound Color (C.) H N 0 H N (HMPA)4La(OSOaCFa):--..:. White 310 24.95.5 12.9 25.0 5.7 12.7 (HJ\/IPA)4Pr(0S0zCFa)s Light green--. 315 24.85.5 12.9 24.7 5.6 12.5 HMPA)4Nd(OSOzCFa)a----- Light violet-.- 320 24.85.5 12.8 24.8 5.6 12.6 HMPA)4Gd(OSOzCF);.-.---- White 307 24.7 5.5 12.724.7 5.6 12.6 (WPADEIKOSOICFQ; -.do 310 24.7 5.5 12.6 24.7 5.6 12.7HIMPA) Y(OSOCF3)3 d0 312 25.9 5.7 13.4 26.0 5.9 13.2 (NMMO)Nd(OSO:CFa)z.---. Light blue 240 28.6 4.7 6.0 28.6 5.0 5.9(NMMO)sPr(OSO2CFa)s Yellow 230 28.5 4.7 5.9 28.9 4.8 5.9(Nh/flMOhLB-(OSOiCFa). White 245 28.6 4.7 6.0 28.4 4.8 5.(NMMO)sEu(OSO1CFa) --d0 245 28.6 4.7 5.9 26.4 4.5 5.1 (NMMO)5Y(OSO:CF3):-.do 235 30.0 4.9 6.2 29.0 4.7 5.8 (NMMO); GG(OSO:CF3)3.-.-Lightye1low.. 260 28.3 4.6 5.9 25.3 4.5 5.1

l Decomposition.

EXAMPLE Neodymium salts are prepared by the above procedure yttriumperfluoromethanesulfonate nonahydrates provides the parameters tabulatedbelow:

using perfluorobutane sulfonic acid, perfluorohexane sulfonic acid,perfluoroethylcyclohexane sulfouic acid, perfluoroethane sulfonic acid,B-hydro perfluoropentane sulfonic acid (C F CHFCF SO H), andfl-hydroperfluoroethane sulfonic acid (CHF CF SO H). These are dried andportions decomposed in argon at 800 C. to give pure neodymium fluoride.The perfluorobutane and perfluorohexane groups are recovered in part asperfluoropropionic and perfluorovaleric acids respectively.

Other lanthanide metals and Group IIIb metals are also converted totrifluoromethane sulfonates, the salts pyrolyzed and the fluoridesrecovered. Suitable metals (in trivalent form) are cerium,praeseodymium, promethium, samarium, europium, gadolinium, terbium,dysporsium, holmium, erbium, thulium, ytterbium, lutecium, yttrium,scandium.

These various fluoroaliphatic sulfonate salts form bydrates and thecomplexes of Example 9 with hetero-atom oxide ligands pyrolyze to puremetal fluorides.

EXAMPLE 11 Roentgenographic study of crystals of neodymium andReferences Cited UNITED STATES PATENTS 3,334,033 8/ 1967 Romanowski eta1. 204-51 DANIEL E. WYMAN, Primary Examiner A. P. DEMERS, AssistantExaminer US. Cl. X.R.

